1. Field of the Invention
The present invention relates to a shape memory polymer composition, a fiber reinforced plastic, and a production process thereof.
2. Background of the Invention
In order to bring materials to space and assemble a structure there, the volume of each material should be kept as small as possible for transportation. For example, a large apparatus such as a solar cell panel to be installed on an artificial satellite or a space structure must be small in size for transport from the earth. An apparatus folded during transport is expanded into a predetermined shape suitable for use in space or on a satellite orbit. The property of a material which permits downsizing for transport action and expansion or development into a predetermined shape for practical use is called “inflatability”.
Inflatability is also an important property for materials used for ground-based structures. Use of an inflatable material makes compact storage (volume reduction) possible for loading on a motor lorry or the like and expansion into a predetermined shape for use at an assembly or building site.
Structures having inflatability can be classified into those making use of mechanical actions such as folding at joints, and those making use of actions based on material properties, that is, restoration into the original shape by heating.
Conventionally inflatability is often realized by means of mechanical structures such as folding at a joint. When used some forces are applied to the joint to expand the structure into a predetermined shape. Such a structure, however, has the drawback that troubles such as disorders or accidents may occur upon expansion.
Several studies have so far been made on structures having inflatability on the basis of a material property. An inflatability material must be rigid and have some strength when it is used for a large-sized structure. Preferred examples of such rigid polymer material having some strength include fiber reinforced plastics (FRPs) and carbon fiber reinforced plastics (CFRPs, which may be included in FRPs). Inflatability may be given by having a fibrous material in a shape memory polymer to form FRPs.
The term “shape memory polymer” as used herein means, among conventional polymers, a resin whose molded shape and deformed shape can be switched by temperature control using heat. A molded product obtained using this shape memory polymer may be deformed at a glass transition point (Tg) or above but below a melting point of the polymer. By cooling it to the glass transition point (Tg) or below while keeping the deformed shape, the deformed shape can be fixed, and then by heating it to the glass transition point or above but below the melting point or decomposition point of the polymer, the original molded shape is recovered. Thus, the deformed shape and the molded shape can be switched by temperature control (refer to, for example, Japanese Patent Application Laid-Open No. 5-320366).
An FRP is generally a fiber reinforced plastic having a continuous fibrous material contained therein. It has a hardness comparable to that of ceramic, has a strength equal to that of metals, weighs about one fifth of iron, and shows a modulus of elasticity about 3 to 4 times as much as that of iron. For such FRP, particularly CFRP, an increased packing density of fibers and a resin per cross-sectional area of it has conventionally been an important research problem.
The proportion of fibers determines the strength of FRP. FRP containing an increased proportion of fibers has excellent strength, but a proper amount of a resin must be added in order to mold or form the FRP into a desired shape such as plate. The resin is also necessary for adhering fibers together. FRP has various kinds, depending on the manner of weaving or twisting of fibers. For example, a cloth of about 10 cm width can be used to form an FRP and such FRP may be utilized to form plates or pipes for large-sized structures.
Upon production of such FRP, a fibrous material must be impregnated with a resin. The fibrous material can be impregnated better with a thermosetting resin than a thermoplastic resin. Since the thermosetting resin usually has a low viscosity and fibers can therefore be easily impregnated therewith, use of it enables the production of FRP having a high quality. In addition, high strength of it can be maintained. When the thermoplastic resin is used, on the other hand, the resin melted into a liquid form has a high viscosity and does not permit smooth impregnation among fibers. In this case, FRP with many voids or defects may result.
When FRP is produced in a conventional manner by using a thermosetting resin having memory shape properties, a two-part curing type resin, for example, may quickly cure upon mixing, and time necessary for impregnation and other operations (pot life) tends to be insufficient.